I've never run deca without test but there are those that do an never face "deca dick".... everyone's different. I usually don't have that problem as long as I have a decent amount of test in the mix.... add some proviron and you're rocketing through!
I had no problem with deca dick when I did stack it with test. Although it did take longer to get a nut never was a big issue. My girl was pleased that I wanted to fuck all the time from the test and couldnt have a quickie if I tried.
Any steroid can cause libido problems. Test is by far not a cure all. Even though I like Test, it shut me down bad when I was younger and did not know any better, With only 250mg for 10 weeks. What you need to do is get your balls producing test with HCG or clomid. thats how you fix your problem.