DFW Controller reported a similar call sign incident that led to an erroneous runway crossing clearance.

Narrative

While working Local East 1; I cleared Aircraft ABCD to land on Runway 35C and subsequently cleared Aircraft ABCH to land on Runway 35C. Several departures were waiting to take off on Runway 35L; so I elected to hold Aircraft ABCD & Aircraft ABCH short of Runway 35L at Taxiway EK. As Aircraft ABCH exited Runway 35C; I cleared the aircraft to cross Runway 35L and to contact ground control. On my 'arrival pad'; I had written down both call signs of Aircraft ABCD & Aircraft ABCH; but confused the call signs in my mind after clearing both to cross. As the first 'echelon' of arrivals crossed Runway 35L; Aircraft ABCH was still short of Runway 35L when I cleared Aircraft Z for takeoff. Aircraft ABCH immediately questioned me; 'Did you want Aircraft ABCH to hold short of Runway 35L'; to which I replied 'Affirmative' then 'Aircraft ABCH; just to verify; Hold Short of Runway 35L -- all while Aircraft Z was commencing takeoff roll. Aircraft ABCH held short of Runway 35L; and I then crossed him after Aircraft Z had departed.First of all; I should have noted the similar call signs of Aircraft ABCD & Aircraft ABCH. Second; I should have NEVER had 2 similar call signs holding short of the same runway at the same intersection--this could contribute to confusion on my part; the flight crew's part; & ground control's part as they cross the runway in tandem. I was so busy getting 'into a rhythm' that I completely forgot that I had marked Aircraft ABCH as an aircraft to which I had issued crossing instructions. After the incident had transpired; I was super cautious about EVERYTHING...which is *exactly* what I should have been doing in the first place!!!!! This incident was unsettling and frightening when I considered it after the fact -- and I requested to be relieved from position to file this report. **Be careful; be careful; be careful** is what I will be doing in the future and certainly not prioritize my 'rhythm' over the responsibility of safely separating traffic