My friends with benefits wants to know why I don’t want a relationship with him. Should I tell him the truth or give a white lie?

I’ve been sleeping with this guy for five months (although I’ve been going on dates with other guys). He’s a cool guy and I enjoy hanging out with him, I just don’t think he’s relationship material. He’d recently been hinting at taking things further and I’d been trying to avoid this conversation like the plague. Yesterday, he finally asked if I’d consider being in a relationship with him. I finally broke down and told him no and that I don’t see that happening. This afternoon he asked why. Truthfully, I just don’t respect him. He’s cheated in most of his relationships and almost brags about how badly he treats other women (i. e: one of his other friends with benefits wants to be in a relationship with him badly and he’s almost proudly stringing her along but sabotages any attempts she makes to leave the situation).

Should I tell him the truth or tell him that “I’m not in the headspace for a relationship”?
My friends with benefits wants to know why I don’t want a relationship with him. Should I tell him the truth or give a white lie?
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