Dna test

So the guy I've slept with after me & my boyfriend broke up. Is saying he doesn't want a DNA test, cause he is a Gemini and he knows the baby isn't his! My boyfriend and I are working things out. We've been together 4 1/2 years. He is saying he'll take a test it's not a big deal to him... But if it comes back not his. The other guy is saying hell no!!! Advice?!? Please no judging!!!