She surprised me

I live in Florida, have a nice swinging pool, I used to swim in college. and at 61 still in great shape. I'm unloading my groceries and my neighbor a young girl. Lisa 22 offers to help. She talks about how hot it is, I invite her over to go for a swim, I tell her I am going to do my laps for exercise. I just bought a new bathing suit, real revealing and thin, I'm in shape so why not show off? She comes over wearing a beach cover-up. I'm in the pool. I get out, she removes the wrap to reveal a tiny two piece, I get an erection, she notices. WOW ! I notice something in her bikini bottom! She says I see you noticed what I noticed in your suit. I don't know what to say, she says I thought you knew I was trans still with my man parts. I say no I had no idea, she's 5 ft maybe 100 lbs. soaking wet and sexy as hell. I say that's fine with me. I go inside to get her a drink, I come out and she is topless, small but nice tits, no tan marks she says, I say I hate tan lines and often tan naked since my yard it so private. You can do it today I don't mind, see I'll do it also and takes off her bottom, she has a small cock but nice. I take off my suite and lay down on the lounge next to hers first moving it close. Of course I get an erection, she smiles I thought you were straight, being married, I tell her I thought so also but seeing you I am getting turned on. She comes over, we kiss and then she starts sucking my cock, and while she sucks I'm stroking her cock, we end up in 69 and I'm sucking my first cock. She tell me she has had sex with my wife and my wife wanted her to seduce me into having sex. My wife wanted a threesome. My wife is away for the day, Lisa makes a phone call and I hear her say he's knows and the sex was great! We have sex my wife, Lisa and myself it's so hot watching them together and I do love sucking her cock and fucking her, she even fucks me.