Girlfriends Mum gave me a handjob

Here's some context, I've been with my girlfriend for nearly 4 years now, and her mum is an absolute milf. Its something I have teased my girlfriend about since I first met her mum, and it's not even a secret as my girlfriend has told her Mum that I think this and they apparently have had a laugh about it. She's petite and athletic slim, smokey sexy with a innocent demeanor and I have fantasised about her for years. 

For about a year or so now she's been going through a rough time with her husband, my girlfriends father in law and has clearly been calling out for attention and wants to feel sexy. Since the potential divorce and knowing that I find her sexy she definitely started playing on it, doing things like coming into her daughters bedroom after just getting out of the shower and only wearing a small towel while me and her daughter are in bed naked. Another time she left her G-string on the floor in her bedroom doorway. And maybe the most sexual was one morning when I was alone in my girlfriends bed as she had to leave early for work, her mum came into the bedroom wearing a silk dressing gown that was loosely tied allowing her cleavage to show. Not only could you see the shape of her nipples through the fabric but she decided to bend over and pick up some of MY boxers giving me a perfect down blouse of her tits before saying "Shall I wash these for you" while sniffing them. Of course I was unbelievably hard by this but I was much too scared to make any kind of move.

There are lots more things she did like that too but ill get stright to the point. She works for herself as a sports massage therapist and has her own massage studio in the garden of the family home. She has given me a 5 or 6 massages since I got with her daughter, usually just my back. However, this time I had overworked my pecks, she offered to give me a treatment and I obviously accepted.

Getting into just my boxers in front of her now felt quite normal, but laying on my back definitely did not. I almost always got an erection when her mum was touching me purely because of who it was rubbing her hands over my body. It was only as I climbed onto the massage bed that I realised this might be an embarrassing issue. Anyway I laid down and she began massaging me, and for a few minutes all was okay, until I felt blood flowing into my cock and could feel it starting to rise.

About 5 minutes passed and I was now fully erect and throbbing from the excitement and shame, I knew she must have seen it but neither of us had addressed the elephant in the room yet.

She was stood at the head of the massage bed working my pecks when she finally broke the silence by saying - "Someone's a bit excited aren't they" to which i felt myself start blushing straight away followed by me saying 'I'm so sorry, I'm just very relaxed right now'

She simply responded "I'm very glad you feel comfortable around me, its normal to become aroused" then casually moved around the side if the massage table and gently pulled out my cock. Neither of us said anything from that point on, she worked my cock with a good grip with her eyes locked on it, only glancing at me a couple of times. I couldn't take my eyes off of her face and before I knew it I was shooting thick ropes of cum onto my belly. She just gave a little giggle and then got some paper towel. I have no idea how long it lasted but I know I came much quicker and more than I normally do.

We've not spoken about it at all since, but she does occasionally catch me looking at her and gives a little smirk.