I wasn't able to gather if you are life partners and live together. Gosh, if you were I imagine this is all the more difficult.

I asked another person in another thread how they felt their relationship was an enrichment of their life. Have you considered this same question?

You indicated you and he were 'young' and that he might be wishing to live a 'young' life with his friends so I question what exactly are the nature of his friendships? Are these chums of his single? Maybe it is the spontinaeity he is yearning for? Is it possible for him to find room for that (reasonably) within the relationship? If this need though crosses your boundaries then too you need to consider that question.