Is it possible after a 15 year vasectomy to get pregnant?

Idk why I feel compelled to share this but I do. My significant other and I were together for 16 months. I moved in with him a month after meeting on a dating website. I had just separated from my husband and moved in with my adult son and his wife.

After a month of living with my son, he asks me to move out because his wife had issues with how I was trying to help rear my 5 year old granddaughter.

Nevertheless, this wonderful man I had met on this dating website opens his home to me. I spent the first few months ill at my partner’s place. Apparently, the move from the Deep South to the Upper Midwest did a number on me.

However, in March, I started feeling very sick to my stomach and vomited a few times. My partner had a vasectomy 15+ years ago and guaranteed me that there was no possible way I could be pregnant but I was.

I preformed a regular, pee on stick with pink lines, and I got a full one bar and a very faint second bar. I couldn’t believe it! Here I am at 45, with a 5 year old granddaughter and I was pregnant.

I told myself I would retest myself in week or so. My period then became late and after 4 days of testing, I started to bleed heavily with horrible cramps.

I didn’t tell my partner, until very recent, and he refuses to believe me. He keeps telling me that they cauterized his sperm tubes. Is it possible after a 15 year vasectomy to get pregnant and at 45? I am really affraid of having unprotected sex with him because he may get me pregnant again.