Partner now seems unable to be monogamous

I met my partner a year ago and was very explicit regarding what I want from a relationship/life. I want a true partnership, a family and monogamy is the only option for me, my mental health and self esteem couldn’t cope with anything else. He freely agreed to this and said all the right things, sick of the single life, wants a family etc. He had poly relationships in the past but said he didn’t want that anymore. A year down the line and this doesn’t seem to be the case anymore but he is making me feel I am the unreasonable one. I don’t believe he has cheated but I can’t be sure he won’t either and use the excuse that he’s ‘poly’. I am doubting myself because I love him but I feel pathetic. How do I tell the truth from the lies?

If he can't be faithful, regardless of what he says, then why bother being with a man after you've already discussed with him, what you expect & need from a relationship. Like any other couple, you guys need to share values & standards as well as have trust and respect for each other, to be able to have any chance of a decent relationship. He can't be one thing, and you the opposite and you expect things to turn out all ok. You can't make this guy be faithful to you but you do have a choice as to who you are with. If this guy loved you, he wouldn't be making you feel unreasonable and you wouldn't have the doubts that you do have.

Maybe he's been faithful. Maybe he hasn't. I think it's a moot point. If he insists he's poly and that he'll never be happy with just one person...okay. That's fine. But you're NOT and aren't okay with your partner being with other people. Both are reasonable-ish positions IMO. But they're not compatible. (And if he's insiting you should be okay with him sleeping with other women, that's gaslighting and NOT COOL.)

Thank you, you’re both right. I struggle with relationships in general as I take everything at face value and the older I get the more I realise that I can’t ever trust that what people say is the truth. Thank you again for replying, back to tinder I guess!