...okay... so you have been seeing him for 3 months?
Next, does he initiate sex? Or you?
Or is it mutual?
Have you even had intimate relations with him?
How is your relationship with him, OVERALL?????
Is it normal/good/nice etc.? Or full of problem and issues and backstories??
Is he over his ex girlfriend???
How is his feelings about you? How are you together???
Is HE bothered by his non-arousal???
Next, it was HIM... that told you that his ex-girlfriend said he was the best she ever had. So.. you do NOT know, if that is 'fact.'
Maybe, he had that problem with her too.
Men... are afraid to admit to intimacy problems....
So... that may or not be true, that his last girlfriend had a great sex life with him.
So... just concentrate on the both of you. If that is possible.
Or ditch him... if you are both just overall not compatible...
or work on it... try different things.
The issue... is probably him... not you.
He may just have had a 'history' of arousal problems... which you do not know about... because you have only been with him for 3 months. That is not long.
And, his previous girlfriend and he, only broke up 1.5 months before he met you.
Maybe too much, too soon.
Maybe he doesn't even know how he feels.
Maybe it is just not a match
Maybe he has arousal issues... that is his alone.... or needs to see a Doctor for.
Regardless... hopefully he is not making this 'your' fault.... as men naturally are real embarrassed about intimacy issues...
I would.... really reconsider... your relationship with him.
He sounds... to have issues.
Not just with you.