What are your ages?
Why does he get into relationships with people who he has no sexual chemistry with?
Does he sleep with other people? do you?
Does he want to split up?
Thank you for that additional info. The good thing is that the two of you don't want to split up, so that means that the relationship can be worked on. There seem to be a lot of underlying issues that may need to be looked at. Since he was molested, it could account for his avoidance of sex (hence not getting involved with someone he's sexually attracted to and his infrequent initiations of sex).
The fact is, the two of you are together...and have been for 2 1/2 years, so there's something thats holding you together, sexual or otherwise. Keeping that in mind, and using that bond to work through this would be best. Consider individual or couples therapy to help sort through things and envelope coping skills and mechanisms for communicating with each other.
As for your sexual prowess, you've been together 2 years, you should know something about what each one of you likes by this time, but if not, consider working on it in one or more of the following ways. Make a list of the things that each of you likes, and write each one on a little piece of paper. Drop those papers in a jar marked love, or lovemaking and each night you are both allowed to pick something from the jar to do to each other. You can use separate jars for each of you, or you can throw them both in the same jar and each of you has to do the things that are picked. Also, you want to improve on your intimacy overall. For example, this Friday, agree ahead of time that there will be no sex, but that Friday night will be an intimacy night. Candles only, music you both like, some finger foods like fruit, cheese, crackers, and whatever you both like to drink, and the minimum amount of clothes. No tv, no phones, no computers. Give each other full body massages, with warm oil....take a bristle brush and brush each others bodies from head to toe. Give each other hand, foot and head massages. Talk to each other, tell each other the things you like about each others bodies, what you like about each other in general and just enjoy that quiet tie existing in a world where it's just the two of you. The simple fact is, you can become more intimate, by making a conscious choice to become more intimate.
I welcome your thoughts, let me know if you want to talk more.
As I have said, I believe there is chemistry there, but because it's not overwhelming, you're thinking it's not there at all. Some of the things I told you to do above are specifically for increasing the attraction and chemistry. This should be something thats done on a weekly basis, even if you're not having sex. If you're asking if there's something that can make you more attractive to him, you have to ask him that and see what he says.