It sounds like he wants to keep you on the line (promising to marry you eventually) while he still shops around.

Maybe you should find out when his next PT therapy is and pay a surprise visit so you can meet this message therapist. OR, you could continue sneaking a peak and see if he plans to meet, when, where, what time and just happen to be there too if it's someplace you can go like a restaurant etc, grab a friend to go with you if you can. Better to catch them in the act so they can't deni.

It is better to know "risks" up front before you get tied into a marriage or anything long term. Yes, it hurts, but better now then when so much more is invested.