tight and loose vagina

He says that sometimes my thing feels tight and sometimes it feels loose as if I had stick something bigger than his thing or as if I had sex with someone with a bigger d 
But I'm not doing none of that. 
I've been doing the kegel exercises for a few weeks now and I can see the difference he says that now it just feels tight
But he thinks I probably cheated on him before and that's why it felt like that 
I don't know how I can explain it to him 
He said none of the other women he's been with had that happened to him 
It breaks my heart to hear him say "I cheated" 
He said he asked around with other women and that they told him I was doing something