Please help me!!!

My 35 year old wife is sooo hot! She's 5'0" 105lbs. Blonde hair, blue eyes, big 36D's that I bought her 5 years ago. All of the men and several of the women she works with have openly told her they want to fuck her. Heres the problem. I have a small penis and have had erection problems off and on for a year or so. My cock is 5 inches and average to slim girth. Tammy has always had a porn stars pussy, and the first time I saw her naked, I spent an hour just licking it. She doesn't like oral that much, but occasionally lets me do it. When she wants to be laid, many times I just cant get hard. I think it is in my mind because I know I am no longer able to satisfy her the way she deserves. I have offered to let her take a lover, but she says she will never be with more than one man at a time. I love her so much, and never want to be away from her, and really want her to be satisfied. When my cock does work, I always talk about her being with a sexy well hung man while I am fucking her, she instantly gets wetter and usually cums very quickly after I start talking about it. During sex, she says she wants it, but sitting outside after work, she says no way! I am a willing cuckold, and I know if she ever gave in she would like it. I need help explaining to her that I only want her, and that as long as I know what she is doing, it isn't "cheating". She is the love of my life, and I do not want to lose her. If I can't satisfy her pussy, I think she will probably end up leaving me someday anyway so what do I have to lose. I was in an open relationship years ago, and loved it so I know I can handle it.
Any suggestions are appreciated!!!

Take it easy! Slowly is the key here. Instead of being so forward easy her into cuckolding you. First bedroom games with her being domiante and you submissive (maybe some commenta about how small you are compared to her fantstay stud). Then intrioduce a big black dildo and slowly stop fucking her (the dildo take over). Give the dildo a name and use that name as her fantasy lover!

When out and about from time -time ask her to comment on how big other guys bulges are.. Play a game like that..

Take it slow man and she will go for it over time

OK. She has a closet full of dildos and has even used large fruits and veggies in the past. My biggest concern is the fact that I can't perform when she wants me to. It breaks my heart that she is not getting what she needs. I do appreciate your suggestion, and will give it a try ASAP.
Thanks

I will try to put up a pic or 2 if I can resize them.

SHE'S GONNA DO IT!!! She got takes Saturday night and begged me to fuck her! While I was doing it I asked her about one of her co workers that I know she is always kissing on the cheek and joking around with. She confessed to me she wants him inside of her. She says she hopes he is much larger than me, and she wants to see his big black cock slide inside her. Tonight I am going to have a long talk with her about how this will all go down. I am soooooo excited!!!