you have mentioned several important things-
1 the man in question having had one night stands and/or multiple shallow relationships
2 he has never been married and possibly seeking to get married to keep up with peer pressure
3 the fact that you have been living apart and/or not seen each other for some time
4 he had had an intimate encounter in June
As far as being able to trust him, that is something you will have to decide. Past behavior is a predictor of future behavior. Hence, if a person had now learned and shown that they are both willing and capable of behaving otherwise, you may continue to run into the same patters with him. The question to ask yourself is what is it that you feel he is going to be able to offer you if not fidelity and honesty in a relationship and if it is worth it.