Guys, Why would a guy in a relationship invite me to his house when his girlfriend is out?

He's living with his girlfriend for years and she's pregnant. We've been friends for months and we work together but I have a feeling there's a lot of sexual tension between us sometimes. He flirts with me ocasionally and we went out alone a few times as friends. Never thought about him more than that, but the other day he said his girlfriend is going to stay gone for the weekend to visit her family and he invited me over to their house to cook dinner for me. So we're going to be all alone.

Should I assume he's just being friendly or does he want more?

Guys, Why would a guy in a relationship invite me to his house when his girlfriend is out?
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