Well, ISFJ's like to be given lots of love and attention. They like to feel that they are somebody to someone else, which is why I would say that a lot of them feel the need to have deep, meaningful relationships. I guess, from a male ISFJ perspective, a male ISFJ would want to feel like he can be a good male to his female companion, which I would say involves being able to fulfill their different needs, emotional, physical, what have you... I think that most ISFJ will feel best if they are allowed to make their partner happy, while at the same time being shown interest and appreciation by their partner. An ISFJ loves to make others feel good, but they equally enjoy it when others taken a special interest in them and when they are shown that the other person really values them and 'needs' them as it were.
Personally, I like SP's a lot. Probably my ideal partner in theory would be an ESFP. I don't say that because a lot of sites and research says so, but because I do feel probably most attracted to those types of personalities. I like SJ's as well though. I can't think of any female ISFP's that I know off hand... Maybe I just don't know them well enough yet... So I don't have any specific ISFP examples. As for particular traits I would look for? I would say I like someone who is cute, classy, affectionate, intelligent with common sense, sensitive, but not overly so, down to earth, someone who takes interest in me and wants to be with me, someone who I could spend the rest of my life with and be my best friend. There's other stuff of course but I mean there's tons of things you could say about what you find ideal.
What I DO NOT like would be trashiness, or 'loose' girls, etc. I also HATE fake people. As in, people who pretend to be something they're not. I know myself, I tend to be more of a traditional person. So, marriage, family, a nice social life, etc. are all things I can appreciate. I doubt all ISFJ's are like this though I do think if there's a type that you could count on to be more traditional, one of them would definitely be ISFJ. I also think that ISFJ's want someone that is looking for a long-term relationship. They are the type that think more of soul/life mates and one person for everybody. I guess they would appreciate someone who has a similar view on that.
Anyways, I guess what it comes down to is that if you show how much you appreciate him and let him feel like he is very important to you, that he is needed, then I think that would probably be the best. Don't go overboard either though, complimenting every little thing that he does for example. Everything within moderation, but know that he will probably have these needs. A little absence makes the heart grow fonder as well. I believe one of the problems for some with ISFJ's is that in general they tend to be clingy emotionally, so that may be a problem, though maybe you like that, ISFJ's obviously do. I think that this comes from the desire to have that super deep relationship with their soul/life mate that will always be there for them and who they want to always be there for. I'd say depending on how Introverted he is though, he will probably enjoy his space once in a while as well. I think it may also depend on how many other close friendships he has as well. ISFJ's need to get that sense of belonging and need, and they don't like to let their other friends down. That means he won't want to let you down either. I think ISFJ's sometimes have a tendency to be perfectionists in some things if they feel they aren't getting their needs fulfilled because they feel they have to do more, or be better in order to get people to like them more. They could feel as if they're not doing what they should. They might do this if they do not get enough appreciation.
A few more things... Another thing some ISFJ's have an issue with I think is control. ISFJ's like to have control of things in their lives. I think that if an ISFJ gets too needy, he may try to control the person he is being needy with more than he should. Everyone tries to exert some control over things people we are close to do... but I think an ISFJ needs to realise this possible danger of being overly controlling. Again, I think that this may have to do with how many other friends and close friendships he has. Also, if ever you have to tell him that he is not doing something right, he may take it badly at first, depending on how he feels. It may either upset him and get him angry or it may make him feel depressed. I think the outcome here depends on whether leading up to the conflict, he feels he has been doing everything right and was criticized all the same (which would make him angry), or on the other hand, he has been feeling down about himself already, or feeling like he is not doing enough and hence feeling that he is 'not good enough' (criticism here I think would make him depressed, possibly angry as well). If you approach him in a mild way, and tell him that calmly and civilly that he needs to change something, then he is probably going to be more willing to listen. Also if he does ever overreact, it might be best to let him cool down before trying to reason with him. When an ISFJ is really upset, I think they tend to really rely on their FEELING trait and do not always listen to reason. If you do the same because you are a Feeler as well, then two opposing sides of feelings might not be the best way to solve a conflict. I think it's best to wait until the ISFJ calms down before discussing things. They often say things they do not really mean, or regret later when they are angry. Just be careful not to get him angry again later when you address the subject by doing things calmly.
I believe that ISFJ's are very affectionate people, especially or at least with the people they are very close to. So he will probably appreciate the right amount of affection in return as well.
Anyway, that's my take on some of the things an ISFJ might be like in a relationship. Obviously everyone's different, even among the same types, so it could be your boyfriend is a little different on some things, but I am an ISFJ male and this might give you some things to think about.
