He is a "cowboy." He says he is fine with being poly, but then once he gets the woman attached to him, he tries to get her all to himself.
Many issues here. He's bad at sex? But good at romance? You're good at sex but bad at romance? Your gf probably wants more. If you were all poly, this could work. Great sex with you, cuddles and movies on the couch with him.
BUT, you both went into this with sort of a swinger mentality. Allowing your partner to only "casually date/fuck" another is not polyamory. Amor means love. Love is encouraged in polyamory, not prevented.
Personally, I dislike people who say, you can fuck, but not love, so-and-so. First of all, isn't so-and-so also deserving of love? Second of all, how do you prevent love when being physically intimate? The hormones that are released during dating (eating together), cuddling, kissing, oral sex and fucking cause intense bonding.
I don't understand people who want the sex without the bond. Unless you are so insecure of your partner's love.... work on trust! Don't try to prevent love. If you don't let her love him she'll have to tamp her feelings down across the board, and might end up loving you less.
Love withers under constraint; its very essence is liberty. It is compatible neither with envy, jealousy or fear. It is there most pure, perfect and unlimited when its votaries live in confidence, equality and unreserve. -- Shelley
Mags (poly, F, 60) loving miss pixi (poly, F, 38) since January 2009, living together since 2013
also loving Punk (monogamish, 42, M) since Oct 2015
"Master," (mono, 34), miss pixi's Dom for 2 years