My need

My girlfriend suffers depression, has her great days, has her bad days, shes very shy and paranoid about her body, think shes ugly and scared she might lose me at any time. she claimed, when we got together that she wasnt highly sex driven but to my surprise, that wasnt true. We dont live together so i see her about 2 days a week, when im not with her i get very highly horny and fantasize about her kissing another woman, this is an ultimate fantasy and as much as fantasy should stay in the head, i really would love to see her and another woman get it on. I know she would instantly say no way, never even tho she has had lesbian encounters in her earlier days, she would be so worried that i would leave her for the other woman which wouldnt happen, but the idea of someone else pleasuring my woman, touching and seeing, kissing parts of her body that none else other then me should be seeing makes my body go on fire. As much as also in my fantasy id love to see her get fucked by another man, in reality im not sure that i could cope, but the insane jealousy would be hot, tho unsure about that fantasy becoming reality, girl on girl is what i want to see so much, I would really like advice on how to bring this up to someone who has mental issues, should i just keep it to myself.