He sounds like an insecure guy who needs to have a girl next to him all the time....I can bet you that this relationships will not last more than couple of weeks even!
If I were you, I would cut the contacts lose with him....and be relaxed....why to bother yourself with none-sense....
I've been there and I've done it....this is long time ago....I was so devastated when I saw him with another girl, just couple of weeks after our break up....such a jerk....well...he went out with that girl just for couple of months and then broke up with her and went out with her best friend....how ugly it is? I'm so glad that he's not in my life....that's who he is....
just my 2 cents advice to you.....don't try even to know what he does, because whatever he does will just hurt your feelings.....if the relationship doesn't work and he's gone out already with another girl, then why to bother yourself....
take care
marjan