First, I'm willing to answer your questions without your paying more money, although I cannot speak to the policies of other experts, so if you use this service in the future, they may have different ideas.
If you decide to pursue your husband's benefits, you do not need to tell him yourself, but Social Security will notify him.
You cannot choose to use only his benefits and not yours. Social Security will pay your social security benefits before paying you your ex-husband's benefits except in the following circumstance:
If you are at "full retirement age" (which varies based on your date of birth but is always at least 65 years old) you can choose to receive only your ex-husband's benefits now and delay receiving retirement benefits until a later date. If retirement benefits are delayed, a higher benefit may be received at a later date because delaying your benefit gives you a higher benefit when you actually start collecting.
The amount of benefits you get on your ex-husband's account has no effect on the amount of benefits your ex-husband or his current spouse may receive. But, in case you are still curious, common law marriage
does exist in Rhode Island so it is possible that the woman he currently lives with might also have some right to his social security retirement benefits.
In order to establish a common law marriage in Rhode Island, a couple must have "seriously intended to enter into the husband-wife relationship." Demelo v. Zompa, 844 A.2d 174 "The parties conduct also must be of such a character as to lead to a belief in the community that they were married." Demelo v. Zompa 844 A.2d 174 "The prerequisite serious intent and belief is demonstrable by inference from cohabitation, declarations, reputation among kindred and friends, and other circumstantial evidence." Demelo v. Zompa, 844 A.2d 174. A crucial element to common law marriage is whether a couple holds themselves out to the community as husband and wife.