My boyfriend and I had shared a flat for about year before I discovered his fetish.
I suspected my boyfriend was masturbating with my knickers when I found on washday that some of my underwear was 'crusty' when I went to put it in the washer. I didn't know how to approach him about it as I found at least a couple of pairs of my knickers each week would be in that condition. I was kind of grossed out but also flattered slightly that my aroma 'aroused' him enough to masturbate.
It all came out about two months ago when I came home from work early. My boyfriend worked shifts and finished at two in the afternoon whereas I usually got home around six pm. On this day I left work around three pm as I had a dental appointment. I entered our flat and kept quiet as he sometimes takes a short nap after getting home from work. I crept up to our bedroom and the door was cracked a couple of inches. I could hear panting and mumbling and thought he must be dreaming. I checked through the gap in the doorway and saw him with his cock in one hand and a pair of my dirty knickers in the other. He was holding them up to his nose and sniffing them whilst wanking. I didn't know whether to laugh or scream at him.
I stood looking through the slightly open door for a while and I could hear him murmuring my name from time to time. I had to admit his cock seemed huge as he stroked it up and down and I felt myself getting a little damp. I snuck my hand up under my skirt and dragged a couple of fingers across my clit over my knickers. I watched for a while longer feeling my own arousal building as my knickers got more damp. At that point I decided to give him a little surprise.
I burst into the bedroom and stood in front of him, hands on hips. 'What the heck are you doing with my dirty knickers' I cried at him. He looked very sheepish and didn't really have an answer. 'Are you wanking with my dirty knickers?' I asked him. He nodded rather meekly and muttered 'Sorry'. 'So, you're a little wanker, are you?' I said rather sternly to him. He nodded in reply as I looked at him with an air of contempt. 'Well you'd better finish what you've started, there's no point in wasting a good hard-on' I said to him. He looked at me not knowing what to do now. 'Go on, you dirty little wanker' I said to him, 'keep wanking that hard cock of yours'. He began stroking again as I continued to deride him, calling him pathetic and a wanker. His cock seemed to grow even more as I carried on verbally abusing him.
I dragged an easy chair towards the end of our bed and sat down with my skirt pulled up, legs wide open and my now damp knickers on show. 'I bet you'd like to sniff these knickers' I said to him as I rubbed myself through the thin material. 'These are nice and damp and sticky by now.' 'I bet they smell real good' I pointed out to him. His hand was a blur as his stroking got faster and faster. I knew he would come soon as I continued to call him a dirty wanker. I pulled my knickers off and threw them at him. He immediately held them to his nose and began shooting several ropes of cum up his chest and abdomen. I plunged a couple of fingers inside myself and felt that tingling sensation down there burst as I orgasmed myself.
Having come down from our respective orgasms, we looked at each other and giggled. What happened next I can't say here, but I never made my dental appointment.