Im trying to put on muscle mass by lifting weights. question is, does masturbating cause muscle loss or the ability to gain muscle?

The latter: Masturbating causes the ability to gain muscle, as masturbating requires movement. Whichever muscles are moving (or working) have ability to gain size, strength, or stamina. Of course, whether or not there is gain depends on how muscles are working, such as longer periods of light muscle work vs. shorter periods of heavy work. For most folks, masturbation-related muscle changes are not noticeable.

Cleveland Clinic: Masturbation is a normal, healthy part of your sexual development. It involves the use of your hands, fingers, sex toys or other objects to stimulate your genitals and other sensitive areas of your body for sexual pleasure. Masturbation has many documented health benefits. It may reduce stress, improve sleep and ease pain, among other benefits.

Masturbation has no affect on muscle mass